I would've never thought to use river rock at the base of potted plants/at the edges of the patio, but maybe that could work. A larger, flat top rock could even act as a riser for a led candle lantern, etc.
Mason Jar Lanterns Hanging Tea Light by TheCountryBarrel on Etsy - easy DIY! Small chain link, mason jars, decorative nonflammable filler and candles! Tap a hole with a nail for the chain to attach to the jar lid. And done!